1. Field of the Invention
The present invention relates to a grinding machine with a rest apparatus capable of keeping a taper amount of a finished workpiece within a reference limit.
2. Brief Description of the Prior Art
In a conventional grinding machine with a rest apparatus, rest shoes of the rest apparatus has been fed toward a workpiece during a grinding cycle and a feed amount of the rest shoes has been controlled by a sizing device for measuring a diametral dimension of the workpiece during the grinding operation. Accordingly, it has been difficult to substantially eliminate a taper of the workpiece which is created during the grinding operation, although the taper is compensated to a certain extent before the finish of the grinding operation. More specifically, elastic energy based upon grinding resistance of a grinding wheel is stored on the rest apparatus. Therefore, even if a deflection of the workpiece is corrected by the feed of the rest shoes during the grinding operation so as to compensate for the taper of the workpiece, the rest apparatus is elastically restored when the grinding resistance becomes small in such a case as a fine grinding operation, whereby the deflection is still left on the workpiece, and as a result, the taper of the workpiece remains unremoved. Furthermore, dispersion of the taper is increased by the change in cutting ability of the grinding wheel. Accordingly, a tolerable accuracy has not been satisfied.
A change in a taper amount of a workpiece ground in the conventional manner within an interval between two consecutive dressing operations is shown in a dotted line in FIG. 4. It is seen that a taper of the workpiece tends to be negative while a cutting ability of the grinding wheel is large, that is, while a number of workpieces being ground is small, and that the taper tends to be positive and to be increased when the cutting ability is decreased. It is assumed from this result that elastic deformation of the rest apparatus caused by the feed movements of the rest shoes and the grinding wheel is restored during the time from the taper compensation grinding to the finish of the grinding, and the workpiece is deflected toward the grinding wheel at the time of the finish of the grinding while the cutting ability of the grinding wheel is large, whereby the taper tends to be negative. It is also assumed that the amount of elastic restoration of the rest apparatus is decreased when the cutting ability is decreased, whereby the taper tends to be positive and to be increased.